The geometries and the harmonic vibrational frequencies for several SNO doublet state isomers have been predicted at density functional theory levels with a 6-311+G* basis set. Results have indicated that there are nine doublet states (five bent, three nearly linear and one cyclic). The ground state corresponds to a bent (2)A' SNO structure. The state-state correlation and the isomerization mechanism are also predicted by searching the transition states and the intrinsic reaction coordinate analysis. Results have indicated that the ground state is the most favorable product. The nearly linear (2)A" SNO state may be obtained from the bent (2)A' SNO state by electron transition. (C) 2003 Elsevier Science B.V. All rights reserved.